What is the religious ruling regarding my return to my wife, whom I divorced with three pronouncements, knowing that a sheikh issued a fatwa that the divorce was bid'i (innovated/unlawful) and therefore not valid, and my mother refuses my return to her for fear of falling into haraam (unlawful acts) and facing people's criticism?

The fatwa adopted by us is that divorce during menstruation or during a period of purity in which intercourse occurred is an effective divorce, despite its being an innovation (bid'ah). This is the view of the majority of scholars. This means that your wife has been irrevocably divorced from you, and she is not lawful for you unless she marries someone else, and he consummates the marriage with her, and then divorces her or dies, and her 'iddah (waiting period) expires.

However, some scholars, like Sheikh al-Islam Ibn Taymiyyah, hold the view that innovative divorce is not effective. There is no objection to acting upon this opinion if you are content with it and are not following your whims. In this case, you are not obliged to obey your mother in refraining from returning to your wife. However, you must honor her, treat her kindly, and strive for her satisfaction. You can seek the help of some righteous people or scholars to clarify the religious ruling to your mother.